Apparatus for compacting permanent magnet powders into pressings



Dec. 17, 1968 H. RICHTER ETAL 3,416,191

APPARATUS FOR COMPACTING PERMANENT MAGNET POWDEHS INTO PRESSINGS FiledMarch 14, 1966 4 Sheets-Sheet 1 7 5' a ooooo o o o 0 000000 OOOOOOO 1968H. RICHTER ETAL 3,

APPARATUS FOR COMPACTING PERMANENT MAGNET POWDERS INTO PRESSINGS FiledMarch 14, 1966 4 Sheets-Sheet 2 7 5' 6 5 7 I JOOOOOO 6 OOOJOOO 0000000 looooooo Fig. 212

1968 H. RICHTER ETAL 3,416,191

APPARATUS FOR COMPACTING PERMANENT MAGNET P OWDERS INTO PRESSINGS FiledMarch 14, 1966 4 Sheets-Sheet 5 7' 5' 5 7 OOOOJOOOOOjJO 0000040000 7' 50 5 7 0(000000900 I OOOJADOOOOOO Fig. 3 b

' In nt0rs Dec. 17, 1968 H. RICHTER ETAL APPARATUS FOR COMPACTINGPERMANENT MAGNET POWDERS INTO PRESSINGS 4 Sheets -Sheet 4.

Filed March 14. 1966 O OOOOOOOOOOO Fig. [111 5 7 /AOOOOOOOOOOOOOOOOOOOOO 7! OKOOOOOOLOOO OOOOOOOOOOOO Fig. 11 b United States PatentOflice Patented Dec. 17, 1968 3 Claims. (Cl. 18-16.5)

For the production of magnet bodies made of barium or strontium ferritewith a preferred direction of magnetisation, the conventional procedureconsists in mixing strontium carbonate and Fe O powder in the proportionof about 1:4, sintering the mixture at a suitable temperature for thepurpose of forming the mixed ferrite crystal, crushing and finallymilling the ferrite material to a fineness under 51.4. This fine-groundferrite powder is then magnetically orientated in presses by theapplication of a magnetic field, pressed to the desired magnet shape andfinally sintered to completion.

The present invention relates to the pressing of the powder in amagnetic field. As known, the ferrite powder is filled into dies eitherin the dry form or in the form of a watery slurry and pressed whilstexposed to a magnetic field in the direction in which the magnet is tobe preferentially orientated. When pressing a liquid material the liquidis withdrawn from the slurry during this process. The direction of themagnetic field may be parallel to or across the pressing direction,permitting the preferential direction of magnetisation of the discs,rings or like to be either axial or parallel to a diameter.

It has also been proposed, besides orientating the powder, to use themagnetic field for magnetically sucking the dry powder or slurry intothe cavity of the die by making use of the inhomogeneity of the magneticfield. When this is done orientation in the crosswise direction cannotbe performed directly after magnetically drawing the powder into the diein pressing direction because the magnetic field between the poleshoesof diametrically disposed magnet coils which would have to be locatedabove the magnet coil required for creating the suction, would naturallyinterfere with the suction field and it would therefore be impossible tosuck the ferrite powder magnetically into the die.

It is the object of the present invention to provide an apparatus inwhich the drawbacks of conventional 'arrangements are overcome and inwhich cross magnetisation can be performed even if the powder ismagnetically sucked into the die. According to the invention the problemis solved by providing a die and a magnet coil which are relativelyaxially displaceable for drawing the powder into the die and a pair ofmagnet coils for generating the field for diametrically orientating thepowder, with poleshoes movable in the radial direction, i.e., normal tothe axis of the pressing tool. This form of construction permits thelatter pair of poleshoes to be withdrawn from the zone of the magneticsuction field whilst the powder is being drawn into the die, so thatthis process is not interfered with. Conveniently, the poleshoes arearranged to be movable into contiguous adjacence with a die which ismade of a nonmagnetisable material and to this end they are axiallymovable inside the magnet coils which embrace them. Alternatively, themagnetic field for diametrically orientating the powder may, if desired,be generated by permanent magnets.

The manner in which the proposed arrangement functions is illustrativelyshown in more or less schematic form in the drawings. In the drawings,FIG. 1a is a sectional elevation showing the apparatus ready for drawingthe material into the die, FIG. 2a is a sectional elevation showing thedie as having risen from the position shown in FIG. 1a and the materialdrawn thereinto; FIG. 3a is a similar elevation showing the poleshoes ina position for producing the transverse magnetisation; and FIG. 4aillustrates the pressing operation after transverse magnetisation. Thefigures whose numbers are provided with index a are all axial sections,whereas those provided with index b are the corresponding plan views.

FIGS. 10/ lb show the pressing tool in the position it occupies beforethe filling operation begins. The punch 1 which consists of or the headportion of which is of a nonmagnetisable material is in its normalposition of rest. In this position the bottom punch 2 and the upper edgeof the suction coil 4 may be brought flush with the upper edge of thenonmagnetisable die 3. The feeding shoe 6 containing the charge offerrite powder is directly above the centre of the die. The poleshoes 5,5' of the diametrically orientating pair of coils 7, 7' are retractedfrom the die sufiiciently to be out of contact with the suction coil 4and not to interfere with the suction field. In the position of thepressing tool illustrated in FIG. la the field coil 4 for generating thesuction is energised whilst the die rises, the coil 4 and the lowerpunch 2 remaining stationary in its position. Because of this relativemotion the suction coil will become disposed away from the upper edge ofthe die and draws in the powder.

FIG. 2a shows the filling process completed. The die has been filledwith powder and the magnetic field of coil 4is therefore switched otf.

In FIG. 3a the feeding shoe has been removed. Suitable devices which forthe sake of greater clarity are not shown in the drawing now advance thepoleshoes 5, 5' through or with the coils 7, 7' into position forapplying the field for diametrically orientating the ferrite powderinside the cavity of the die. In this position the poleshoes aresubstantially in direct contact with the die. Consequently the fieldwhich arises when the coils are energised is particularly intense.

FIGS. 4a and b show the manner in which the powder, after orientation inthe direction normal to pressing direction, is compressed.

It will therefore be seen that the proposed arrangement, by usingsuitably shaped dies, which may be dished, annular or bar-shaped, andwhich may be ditficult to fill when the wall sections of the pressingsare thin, is capable of conveniently pressing the magnet bodies incontinuous production by drawing the powder into the die in conventionalmanner by magnetic suction and nevertheless magnetically orientating thepressings in the diametral direction, i.e. across the pressingdirection. The arrangement is principally envisaged for use in theprocessing of ferrite powder. However, in principle the arrangementwould be as readily applicable to the processing of other powderedpermanent magnet materials.

What we claim is:

1. Apparatus for compacting permanent magnet powders into pressingmagnetised diametrically across the pressing direction in a die intowhich the powder is introduced by magnetic suction, comprising the dieand a magnet coil which are relatively movable in the axial direction ofthe die for drawing the powder into the die References Cited UNITEDSTATES PATENTS 2,959,823 11/1960 Schwable et a1. 264-24 I. HOWARD FLINT,

4 Falk et a1. 1816.5 X

Gordon 264--24 Biittner et a1.

Quinn 18-16 Miiller 18--16.5 X

JR., Primary Examiner.

US. Cl. X.R.

1. APPARATUS FOR COMPACTING PERMANENT MAGNET POWDERS INTO PRESSINGMAGNETISED DIAMETRICALLY ACROSS THE PRESSING DIRECTION IN A DIE INTOWHICH THE POWDER IS INTRODUCED BY MAGNETIC SUCTION, COMPRISING THE DIEAND A MAGNET COIL WHICH ARE RELATIVELY MOVABLE IN THE AXIAL DIRECTION OFTHE DIE FOR DRAWING THE POWDER INTO THE DIE AND A PAIR OF MAGNET COILSWITH POLESHOES MOVEABLE CROSS-